Field of the Invention
This invention pertains to boron carbide materials and their preparation that are advantageously employed in thermoelectric applications. Although the boron carbide of the invention finds applications in both logic and spin applications, the particular environment to which the p and n-type boron carbide materials of the invention disclosed herein are particularly suited to thermoelectric converters and similar devices.
The boron carbide devices of this invention can be built on virtually any substrate, although conventional metal are preferred. As set forth in U.S. Pat. No. 7,368,794, incorporated herein-by reference, aluminum, nickel, gold, silver, copper or cobalt as convenient substrates may be used, once cleaned and then placed in a suitable chamber. Silicon may also be used as a substrate, and metal combinations with PMDA-ODA (Kapton).
Related Art
A great deal of attention has been focused on the formation of boron carbide, both doped and undoped, as a suitable material for use in semiconductor devices, particularly when mated with silicon. In U.S. Patent Application Ser. No. 61/494,610 also incorporated herein-by-reference, we disclose the provision of boron carbide based thin alloy films formed from UHV deposition. In the examples, copper was used as the substrate, but other substrates can be used. Orthocarborane and 1,4-diaminobenzene are introduced into the deposition chamber according to the details provided in the pending patent application. The deposited films are a characteristic of p-type semiconductors. Of particular importance for the application discussed herein, conductivities in these boron carbide alloy films are considerably higher than those encountered in conventional semiconducting boron carbide films. The UHV method also lends itself to the inclusion of relatively high amounts of dopant, by introduction into the chamber.
Other methods of forming boron carbide films on a useful substrate are known to those of skill in the art. In particular, U.S. Pat. Nos. 5,658,834, 5,468,978 and 4,957,773 all incorporated herein-by-reference, disclose the formation of boron carbide semiconductor films, and devices made thereby, from carborane precursors. In particular, the precursor carborane is preferably closo-1,2 orthocarborane, closo 1,7 metacarborane and closo 1,12 paracarborane. These boron carbide films are in general p-type films.
U.S. Pat. Nos. 6,025,611, 6,440,786 and 6,600,177, each of which is incorporated herein-by-reference, also describe the formation of boron carbide films, and importantly disclose that these films may be doped by incorporation of a suitable source material in the plasma chamber in which the plasma enhanced chemical vapor deposition of the boron carbide films occur. Although, as noted, boron carbide films prepared from orthocarborane sources are in general p-type materials, sufficient dopant (nickel in the examples) can be included in the formation gases to convert the boron carbide formed to an n-type material. Almost one percent (1%) nickel can be included before it precipitates in the formed film (forms aggregates or “clumps).” Other potential dopants, including chromium, manganese, iron, cobalt and ruthenium are discussed.
U.S. Pat. No. 6,771,730 is directed to a neutron detector, as is the principle application of previously discussed U.S. Patent Application Ser. No. 61/494,610. The entire disclosure of U.S. Pat. No. 6,771,730 is incorporated herein-by-reference. In this device, the boron carbide is formed as an electrically active component of the device, paired with a silicon component on which the boron carbide may be formed, the silicon being an n-type conductor and the boron carbide, as formed from orthocarborane sources, is a p-type layer. Both layers may be doped to accentuate their orientation.
In U.S. Pat. No. 6,774,013 the formation of naturally n-type boron carbide from the meta carborane (1,7-dicarbadodecarborane) is disclosed. The entire disclosure of U.S. Pat. No. 6,774,013 is incorporated herein by reference. To accentuate the n-type character of the boron carbide, plasma enhanced chemical vapor deposition may be used, which it is disclosed, makes the incorporation of n-type dopants, such as nickel, chromium, iron, cobalt and manganese further easily incorporated.
U.S. Pat. No. 7,368,794, also incorporated herein-by-reference, is directed to the formation of neutron detectors, and similar kinetic energy to electricity devices and that disclosure is incorporated herein by reference. In particular, this patent is directed to devices employing an n-type boron carbide and a p-type boron carbide as the two members forming a heteroisomer junction. Boron carbide, in particular, is particularly well suited to high temperatures and harsh conditions, where other semiconductors may fail. It is resistant to radiation damage. A variety of factors make it desirable to employ boron carbide where such conditions may be present.